1. Field of the Invention
The present invention relates to apparatus designed to be employed in the construction or operation of oil and gas wells. More specifically, the present invention relates to a new and improved hydraulically set, retrievable packer and removable gravel pack apparatus designed to be run as a unit in an oil or gas well. The gravel pack and packer are employed to position gravel or other filtering material in the annular space between a screen carried by the packer and the walls of the surrounding well bore. The gravel acts to support the unconsolidated formation surrounding the well bore and simultaneously filters out fine sand and other solid particles so that relatively clean fluids enter the production tubing through the screen.
2. Description of the Prior Art
It is conventional in prior art practice to employ permanent packers which after being set in the well bore may be removed only by milling or other techniques which effectively destroy the packer for subsequent use. Such permanent packers are desirable to the extent that they are capable of providing relatively large axial openings because of their slimline construction and are also able to provide a reliable seal against pressure exerted from either above or below the packer seal. However, to the extent that milling and other means required to remove permanent packers are time consuming and expensive and prevent further use of the packer, such packers are objectionable.
Retrievable packers commonly found in the prior art overcome certain of the problems associated with permanent packers but are objectionable in that the release mechanisms employed often require a reduction in the central opening extending through the packer. Moreover, retrievable packers often do not function as well in providing a positive pressure seal against pressure exerted from both above and below the packer seal, and are difficult to release once having been set. Releasable packers requiring extensive rotational movements to effect either release of a tubing string or release of the packer's setting mechanism are undesirable in that the large torsional forces developed may cause damage and injury if suddenly released through inadvertence or structural failure.
A common problem often found with retrievable anchoring mechanisms set in a well conduit stems from the difficulty encountered in separating wedged slips and spreaders following anchoring of the components. In such devices, complete separation of slips and spreaders must be effected before the slips are permitted to retract radially away from anchoring engagement with the surrounding well conduit. Because of the high forces employed to set the anchoring assembly initially, such separation may become extremely difficult to effect.
In gravel pack equipment, retrieval problems are associated with the release means in prior art apparatus designed to be removable from a set packer. Where such release requires disconnection of threads engaged between the gravel pack and packer, undesirably large twisting forces may be required to produce the necessary separation.
Another shortcoming associated with certain prior art gravel pack designs includes their inability to permit pressure testing of the set packer below the packer seal. Conventional gravel packs of the type where the packer carries a packing screen and is set by the pressure supplied through a tubing string also lack suitable provision for removing debris from the internal portion of the screen by circulating fluids without the use of auxiliary equipment employed after the gravel pack is removed from the packer. Many of these shortcomings stem from the limited number of flow passages and the limited controls for regulating flow through passages found in prior art systems.
Because of the need in a retrievable system for axial and rotational movements to effect the desired setting, release, and passage opening and closing in assemblies of the present type, it is necessary that suitable safety latching and locking provisions be included in such assemblies to prevent inadvertent or undesired movements in the assembly. Prior art devices which have employed such locking and latching mechanisms have often required relatively complex and bulky components which in many cases have proved unsatisfactory or unreliable.
One prior art system employs a combined packer and gravel pack apparatus which employs hydraulic pressure to set the anchoring mechanism in the packer and a vertical movement of the tubing string to open a cross-over flow passage. Preferably, however, setting of the anchoring mechanism and opening of the cross-over passage is effected by simply applying hydraulic pressure through the supporting tubing string whereby slips are set and the cross-over is opened by the same hydraulic action. By this means, setting of the packer and opening of the cross-over passages is effected in a single step rather than in the two-step operation of pressuring followed by axial movement of the tubing string. It is also desirable that the setting and subsequent anchoring engagement of the packer be independent of the weight of the tubing string to which the gravel pack apparatus is secured. This is particularly so where the gravel pack apparatus is to be removed from the set packer after the gravel packing operation has been completed.